The present invention relates to a multiprocessor system, more particularly to a multiprocessor system suitable for use in an electronic switching system.
Electronic switching systems may, for example, be roughly divided into network portions which actually perform the circuit switching or packet switching and processor portions which manage the network portions and perform call processing control. The present invention particularly relates to the latter processor portion.
This processor portion may fundamentally be a single processor, but when the electronic switching system is large in scale, the network portion also becomes large, and accordingly a plurality of processors are introduced. These processor include several secondary processors and a main processor for exercising overall control over the secondary processors, which all together make up a single multiprocessor system. To improve the reliability of the multiprocessor system, the technique of duplexing is introduced. That is, the constituent elements (processors and buses) are duplexed into a 0 system (active system) and 1 system (standby system), with one backing up the other.
The above method of system construction is based on the so-called "one-machine concept", and is extremely flexible with regard to changes from a single processor to multiple processors and further to a duplex construction. For example, it is an extremely efficient method of coping with enlargements of scale of private branch exchanges (PBX). Therefore, it is considered that such multiprocessor system will come into wide use in the future.
As explained above, for duplexed multiprocessor systems, in an electronic switching system, there are single management processors (the aforementioned main processors) and pluralities of call processors (the afore-mentioned secondary processors for call processing), all of which are duplexed. In such as case, the switching of systems among the 0 system and 1 system processors is an important operation. In the past, the method used for this system switching operation was to grant the right to system switching to the call processors. In other words, any call processor could select the 0 system or 1 system.
According to the conventional method for system switching of the duplexed multiprocessor system, for the order of control among the call processors and the management processors, the software had to be managed each time the call processors exercised the system switching rights. In the end, this resulted in the disadvantage of complicating the software management.